The present invention relates to an apparatus for diagnosing a failure or breakdown of an evapopurging system for adsorbing evaporated fuel (vapor) of an internal combustion engine to an adsorbent within a canister and purging the adsorbed fuel to an intake system of the internal combustion engine under a predetermined operation condition for combustion.
For the purpose of preventing the fuel (vapor), that has been evaporated within a fuel reservoir, from being discharged to the atmosphere, there are some internal combustion engine provided with an evapopurge system for once adsorbing the vapor in a canister and sucking the adsorbed fuel to an intake passage during the travel of the vehicle to thereby burn the fuel.
In such internal combustion engines provided with the evapopurge system, since the purge passage from the fuel reservoir through the canister to the intake passage would be damaged due to some causes, or the vapor would be discharged to the atmosphere in case of the separation of the piping system, in order to avoid such defects, it is necessary to diagnose whether there is any breakdown of the evapopurge system or not. To meet this requirement, in general, the internal combustion engines having the evapopurge system is provided with a failure diagnosing apparatus.
A conventional failure diagnosing apparatus for an evapopurge system is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 5-125997. The principle of many conventional failure diagnosing systems is that, after the interior of the vapor passage is kept under the negative pressure condition, the vapor passage connecting the canister and the intake passage to each other is interrupted to define the fuel reservoir, the canister and the vapor passage into a single closed space, and the presence/absence of the failure is diagnosed by a pressure change in the closed space.
In other words, the pressure in the above-described closed space changes when time lapses, however, in the case where there is no failure or breakdown in the vapor passage, the pressure change rate is low to thereby keep the negative pressure condition. In contrast, in the case where there is any failure or breakdown in the vapor passage, the pressure change rate is high and in addition, the internal pressure of the closed space is close to the atmospheric pressure.
Accordingly, it is possible to judge that there is a failure or breakdown if the pressure level within the closed space is in a predetermined range (atmospheric pressure.+-.set pressure), after elapsed a predetermined period of time (set period) since the formation of the closed space. Also, it is possible to judge that there is no failure or breakdown if the pressure level is out of the range.
However, in such an evapopurge system, there is a fear that, if the failure diagnosing process is performed when the fuel is supplied to the fuel reservoir during the operation of the internal combustion engine, such a wrong diagnosis is made that the failure is present in spite of the condition that there is no failure or breakdown.
In other words, when the diagnosis process is performed during the operation of the internal combustion engine, if the fuel supply gun is inserted into a fuel supply inlet of the fuel reservoir, the atmospheric air is supplied to the fuel reservoir tank, the closed space formed for the failure diagnosis is opened so that the pressure within the closed space is substantially the same as the atmospheric pressure. In this case, since the pressure behavior of the closed space shows the same process as in the case of the breakdown of the vapor passage, the failure diagnosing apparatus judges that there is any failure or breakdown.
Incidentally, there has been proposed a conventional failure diagnosing apparatus for an evapopurging system, in which the presence/absence of the breakdown is judged on the basis of the temperature change of the canister instead of the presence/absence of the breakdown on the basis of the behavior of the pressure within the closed space. In this system, the phenomenon that the temperature within the canister is elevated when the adsorbent adsorbs the evaporated fuel is utilized. When the vapor passage is damaged so that the evaporated fuel is caused to flow through the failure part, the amount of fuel adsorption by the adsorbent is small. Accordingly, the temperature elevation rate of the canister is low. The system bases on this phenomenon.
By the way, since the large amount of evaporated fuel is present during the fuel supply and is adsorbed to the canister, even if the failure is present in the vapor passage and the fuel is discharged to the atmosphere therethrough, the amount of the vapor generated from the supplied fuel is larger to thereby elevate the canister. As a result, even in the failure diagnosing apparatus for judging the presence/absence of the failure while supervising the temperature change of the canister, when the failure diagnosis is performed during the fuel supply, there is a fear that a wrong diagnosis that there is no failure or breakdown would be made even if there is a failure or breakdown.